The Delayed “Sea Breezes” in the Sacramento Valley and the Resulting Favorable Conditions for Application of Pesticides

Abstract

Hourly wind recordings at Davis and Grimes, California, revealed that spraying operations by aircraft in summer can frequently be extended beyond the customary sunrise hours without damage by drift to adjacent crops susceptible to the spray material. The data permitted scheduling spraying according to wind types. These wind records also revealed noteworthy meteorological peculiarities. The influx of the marine air beginning in the afternoon lasts almost all night, only being replaced by the opposite flow after sunrise. This indicates that the often heard “land and sea breeze” term is not appropriate, and that rather a monsoon flow tendency prevails. It is suspected that the daily variation is primarily influenced by a daily cycle in strength and northward extension of the Arizona Low.

Diurnal Evolution of Three-Dimensional Wind and Temperature Structure in California's Central Valley

“…Because the synopticscale flows are usually weak, the primary flows in the region are produced by differential heating between water and land and between the valley and surrounding mountain ranges. According to previous studies (Schultz et al 1961;Frenzel 1962;Hays et al 1984;Moore et al 1987;Zaremba and Carroll 1999), the prevailing summertime wind pattern is dominated by marine air that penetrates through the Carquinez Strait, moves through the delta region, and splits into two currents flowing north and south into the Sacramento and San Joaquin Valleys, respectively. Superimposed on this dominant flow pattern are diurnally varying, thermally driven local circulations that flow up the mountain slopes during the day and down the slopes at night.…”

Research and Development of Chemical Distribution Equipment for Agricultural Aircraft in California

“…Another principal factor related to the extent and distance of spray drift is the micro-meteorology of the specific area in which the application is being made (5 >. Obviously wind velocity and direction are pertinent; equally important, although less obvious, are temperature gradients and air humidity, both of which vary widely in Californian agricultural areas during the cropping season.…”

“…Rotary atomisers, initially of brush and disc design (5) , but subsequently superceded by a rotating cage device (1) , have for some while been used with fixed-wing aircraft for producing relatively finely dispersed homogeneous liquid sprays. Common to all these types is rotation in the vertical plane with axial liquid feed intended to give uniform discharge from the rotor periphery.…”

Entrainment Rates and Their Synoptic Dependence on Wind Speed Aloft in California's Central Valley

“…This onshore wind is mostly blocked because the shallow coastal marine boundary layer typically lies below the elevation of the coastal mountains. Nevertheless, the flow is able to inundate the interior of the state at breaks in the orography such as the Petaluma Gap and especially the San Francisco Bay area, feeding through the Carquinez Strait into the Central Valley (Schultz et al 1961;Frenzel 1962;Moore et al 1987;Zaremba and Carroll 1999). This flow is augmented by the extreme land-ocean thermal contrasts found throughout the region.…”